Correlations of Some Saudi Arabian Crude Cuts Physical Properties

Transcription

1 JKAU: Eng. Sci., vol. 4, pp (1412 A.H.l1992 A.D.) Correlations of Some Saudi Arabian Crude Cuts Physical Properties M.H. AlLAN, M.A. GASHGARI, Y. YORULMAZ and H. BAMUFLEH Department of Chemical and Materials Engineering, Faculty of Engineering, King Abdulaziz University, Jeddah, Saudi Arabia. ABSTRACT. The physical properties, such as molecular weight, specific gravity and cumulative volume of both light Arabian and heavy Arabian crude oil cuts, can be correlated with their boiling points if the incremental volumes (TBP distillation) are known. The data obtained experimentally were fitted by using multiple regression analysis technique to predict the various cuts properties. In general, the obtained correlations predicted the various 'properties within acceptable accuracy limits. The correlations predictions also agreed well with other relevant data reported in the literature. 1. Introduction Crude oil is a mixture of a large number of hydrocarbon compounds with each compound having its own boiling point. Therefore, there are ranges of boiling points when a sample of crude oil is heated to successively higher temperatures. As the crude oil temperature is raised, a point is reacl1ed where boiling starts which is known as the initial boiling point (I.B.P.). As temperature increases, butane and lighter components will vaporize first from, the I.B.P. to just below 38 C. The next higher fractions- are called straight-run gasoline, naphtha, kerosene and gas oil which will... Dr. M.H. Ajlan is presently working with the Saudi Arabian Marketing and Refining Company (SAMAREC) on loan basis. 83

2 84 M. H. Ajian et ai. vaporize at different temperatures ranging from about 40 C to 350 C. All those cuts are obtained when distillation is carried out at atmospheric pressure. The rest of the crude is defined as the residue cut which is then vacuum distilled[1]. Molecular weights of petroleum cuts are important in the petroleum industry for the purpose of design as well as for process operations. Several indirect methods have been proposed for correlating the molecular weight with other more readily measured physical properties such as specific gravity and temperature[2]. Maxw'ell[3] proposed a correlation in a graphical form for determination ofmolecular weights of petroleum fractions as a function of mean average boiling point temperature ( Tm) and specific gravity. The API Technical Data Book[4] gives the following relationship for the molecular weight of a virgin (unfinished) petroleum fraction MWT=A x etm x eb(spgr) x (Tm)C x (SP GR)d (1) where T m is the mean average boiling point and SP GR is specific gravity at 60/60 F for the cut. A, b, C and d are constants. Adler and HaU[S] and Hugginsr6] have applied equation (1) on a wide range of temperatures and specific gravities to predict molecular weight. Riazi and Daubert[7,S] have developed the following correlation for the molecular weight prediction of pure hydrocarbons MWT = A x (Tb)C x (SP GR)d (2) where T b is the absolute boiling point and A, c and d are constants to be empirically determined. When applying Eq. (2) to petroleum fractions, Riazi and Daubert[S] recommended the use of ASTM 10 % temperature instead ofthe mean. average boiling point ( Tm ) of the cut. Regarding the cumulative volumes of crude cuts, some graphical. prediction methods are recommended by API. However, no empirical or analytical correlation was found in the literature to describe the b.ehaviour of cumulative volumes as a function of temperature. 2. Experimental The light (36 API) and heavy (27 API) Arabian crude oil samples, provided by Jeddah Oil Refi.nery Company (JORC)., were distilled using a true boiling point (TBP) distillation apparatus according to procedures prescribed in ASTM standards. Each time a sample in the amount of four liters was loaded and atmospherically distilled producing about 40% of the feed as overhead products. Also the obtained cuts were further analyzed in JORe laboratory facilities to determine their specific gravities and estimate their molecular weights.

3 Correlations ofsome Saudi Arabian The specific gravity of each cut was determined using a hydrometer. The molecular weight value for each cut was estimated from its specific gravity and mean average boiling point temperature, by using standard molecular weight charts{9]. The obtained data are presented in Table 1 and 2. TABLE 1. TBP distillation data of light Saudi Arabian crude oil. Cut range 0/0 Cumulative Specific gravity Molecular C volume at 15 C weight TABLE 2. TBP distillation data of heavy Saudi Arabian crude oil. Cut range 0/0 Cumulative Specific gravity Molecular C volume at 15 C weight ;, l60-l Each cut was further distilled to obtained percentage cumulative volume data. Sample data are given in Table 3 for the cut with boiling temperature range of C. The percentage cumulative volumes were correlated as a function of the mid-cut temperature ( Tmid) for the two crude oil cuts. The best fit was obtained in the following form V == A + B x (Tmid)C + D x (T mid )2 + E x In T mid (3) where V is the percentage cumulative volume, T m1d in C, and A, B, C, D and E are constants.

4 86 M.H. Ajlan et al. TABLE 3. Distillation data of the loo-120 C cut for the light and heavy Saudi Arabian crude oils. Percentage Light Heavy crude cumulative volume Temp. DC Temp.oC I.B.P F.B.P No single correlation was found which would fit both the data of light and heavy Saudi Arabian crude oil cuts, therefore two sets of constants are recommended for equation (3) which are presented in Table 4. When the mid-cut temperature (T mid ) is not available for a certain petroleum cut, the following equation is recommended for estimating Tmid in K as a function of the cut's API T mid = (API) (API) (4) Regarding the molecular weight, equation (2) which was recommended by Riazi and Daubert[8] was used to fit the experimental data of this work. The best fit of the equation for both light and" heavy Saudi Arabian crude oil cuts is as follows MWT = x 10-5 (T m )2.405 (SP GI!-) (5) where Tm is the mean average boiling point temperature of the cut in K, and SP GR is the specific gravity of the cut at 150 C. Here again, when the mean average boiling point temperature ( T m ) for a certain cut is not available, the following equation is recommended for estimating Tm in K as

5 Correlations ofsome Saudi Arabian a function of the cut's API TM = (API) (API) Equations (3) through (6) were developed by applying regression analysis technique to the experimental data of this work. TABLE 4. Values of constants for equation (3). Parameter Light crude cuts Heavy crude cuts A B C D x ] X 10-4 E Discussion EquaJion (3) predicted the percentage cumulative volumes of various cuts obtained in this study for both light and heavy Saudi Arabian crude oil cuts with average absolute deviation (AAD) values of 0.570/0 and 1.12% respectively. The results are presented graphically in Fig. 1. Further testing ofthe equation to check its applicability was performed on data provided by lorc and Saudi Arabian Oil Company (Saudi ARAMCO). The equation predicted the experimental data of lorc with AAD values of 5.73 % and 4.170/0 for light and heavy Saudi Arabian crude oils cuts respectively. The Saudi ARAMCO data on the other hand were predicted by the same equation with AAD values of 5.38 % and 2.090/0 for light and heavy Saudi Arabian crude oil cuts respectively. 40 (6) 0 [lcp. (light) 6 [,cp. (heavy) JO Predicted by eqn (J) L.J I: ; Lo.J > <.. 20 == E " 10 40' tono-cut T[MP(RAIURrDC FIG. 1. Comparison of experimental and predicted percentage cumulative volumes.

6 M. H. Ajlan et al. These results prove the general applicability of equation (3) for the prediction of the percentage cumulative volumes of light and heavy Saudi Arabian crude oil cuts within acceptable limits. Equation (4) predicted the mid-cut temperature ( Tmid) for light and heavy Saudi Arabian crude oil cuts with AAD value of 1.17 % Equation (3) and equation (4) could be coupled to predict the percentage cumulative volume provided that the cut's specific gravity or the mid-cut temperature is known. Equation (5) predicted the molecular weight values of the various light and heavy Saudi Arabian crude oil cuts obtained in this study with an AAD value of 1.53 % Equation (1) which is recommended by the API \vas applied for molecular weight prediction of both light and heavy Saudi Arabian crude oil cuts. The predicted values were within an AAD value of 8.20 % The predictions by both equations (1) and (5) are graphically presented in Fig. 2. As seen from the figure and from the average absolute deviation results, equation (5) which is recommended by this work gives better predictions for the tested Saudi crudes than the API equation Pred. by eqn (1 ) Pred. by eqn (4 ) [slimaled L..I 140 C::" < :;:, ụ.. ::r: =' S0 HID-CUT TEHPERA1UREoC FrG. 2. Comparison of estimated and predicted molecular weight for Saudi Arabian crude cuts. Further testing of equation (5), which was performed on the data reported by Amin et al. [10,11,12), confirmed its general applicability. The AAD value of predicting those reported data is 3.86 % Equation (5) can also be easily applied to predict various Saudi Arabian crude oi cuts specific gravity values if the molecular weight and Tm of the cut are known.

7 Correlations ofsome Saudi Arabian When equation (5) was applied for the prediction of the experimentally determine specific gravity values for both light and heavy Saudi Arabian crude oil cuts, an AAD value of 0.53% was obtained. Equation (6) predicted the mean average boiling point temperature for light and heavy Saudi Arabian crude oil cuts with an AAD value of 1.05 % This equation coupled with equation (5) is helpful for the estimation of molecular weight of light and heavy Saudi Crude Oil cuts when only the specific gravity of the cut is known. 4. Conclusion The percentage cumulative volume, the molecular weight, the specific gravity, the mid-cut temperature and the mean average boiling point temperature of light and heavy Saudi Arabian crude oil cuts can be easily and accurately predicted by the correlations developed in this study. The resulting accuracies of predictions were generally within acceptable limits and can be safely recommended for use. Acknowledgement The authors would like to extend their utmost appreciation to Jeddah Oil Refinery Company for providing the crude oil samples and laboratory facilities which were necessary for this work. References (1) Berger, B.D. and Anderson, K.E., Modern Petroleum Technology, 2nd edition, Penwell Publishing Company, Tulsa, Oklahoma (1981). [2] Gruse, W.A. and Stevens, D.R., Chemical Technology ofpetroleum, 3rd edition, McGraw Hill Book Company, New York (1960). [3] Maxwell, J.B., Data Book on Hydrocarbon Application to Process Engineering, 9th edition, D. Van Nostrand Company, Canada (1950). [4] American Petroleum Institute, Technical Data Book, Procedure rd Edition (1980). [5] Adler, S.B. and Hall, K.R., Use Correlation for Oil Properties, J. Hydrocarbon Processing, 64 (11): 7] (1985) [6] Huggins, P., Program produces wide range of distillate properties, Oil & Gas J., Nov. 30: (1987). [71 Riazi, M.R. and Daubert, T.E., Simplify property predictions, J. Hydrocarbon Processing, 59 (3): 115 (] 980). [8] Riazi, M.R. and Daubert, T.E., Predicting flash and pour points, J. Hydrocarbon Processing, 66 (9): 81 (1987). [9] IP Standard for Petroleum and its Products, Great Britain in the Whitefriars, London and Tonbridge Press Ltd. (1983). (10] Amin, M.B., Beg, S.A. and Hussain, I., Arab heavy crude study on kinematic viscosity. Oil & Gas J., Feb. 20: 58 (1984). [11] Beg, S.A., Amin, M.R. and Hussain, I., Characterization of arab medium crude fractions with emphasis on kinematic viscosity - temperature behaviour, J. Fuel Science & Technology, 4 (3): 287 (1986). [12] Beg, S.A., Amin, M.B. and Hussain, I., Characterization of Arab berri (extra light) crude fractions with emphasis on kinematic viscosity-temperature behaviour, J. Fuel Science & Technology, 6 (3): 291 (1988).

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